Imperial College London

DrAnnaRegoutz

Faculty of EngineeringDepartment of Materials

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2.M14Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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74 results found

Fernando NK, Cairns AB, Murray CA, Thompson AL, Dickerson JL, Garman EF, Ahmed N, Ratcliff LE, Regoutz Aet al., 2021, Structural and Electronic Effects of X-ray Irradiation on Prototypical [M(COD)Cl]2 Catalysts., J Phys Chem A, Vol: 125, Pages: 7473-7488

X-ray characterization techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray-induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever-increasing brilliance are developed. In this paper, systematic studies of X-ray-matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complementary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray-induced effects in transition-metal catalysts and, consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.

Journal article

Kalha C, Fernando NK, Bhatt P, Johansson FOL, Lindblad A, Rensmo H, Medina LZ, Lindblad R, Siol S, Jeurgens LPH, Cancellieri C, Rossnagel K, Medjanik K, Schonhense G, Simon M, Gray AX, Nemsak S, Loemker P, Schlueter C, Regoutz Aet al., 2021, Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 33, ISSN: 0953-8984

Journal article

Kalha C, Bichelmaier S, Fernando NK, Berens JV, Thakur PK, Lee T-L, Gutiérrez Moreno JJ, Mohr S, Ratcliff LE, Reisinger M, Zechner J, Nelhiebel M, Regoutz Aet al., 2021, Thermal and oxidation stability of TixW1−x diffusion barriers investigated by soft and hard x-ray photoelectron spectroscopy, Journal of Applied Physics, Vol: 129, Pages: 1-15, ISSN: 0021-8979

The binary alloy of titanium-tungsten (TiW) is an established diffusion barrier in high-power semiconductor devices, owing to its ability to suppress the diffusion of copper from the metallization scheme into the surrounding silicon substructure. However, little is known about the response of TiW to high-temperature events or its behavior when exposed to air. Here, a combined soft and hard x-ray photoelectron spectroscopy (XPS) characterization approach is used to study the influence of post-deposition annealing and titanium concentration on the oxidation behavior of a 300 nm-thick TiW film. The combination of both XPS techniques allows for the assessment of the chemical state and elemental composition across the surface and bulk of the TiW layer. The findings show that in response to high-temperature annealing, titanium segregates out of the mixed metal system and upwardly migrates, accumulating at the TiW/air interface. Titanium shows remarkably rapid diffusion under relatively short annealing timescales, and the extent of titanium surface enrichment is increased through longer annealing periods or by increasing the bulk titanium concentration. Surface titanium enrichment enhances the extent of oxidation both at the surface and in the bulk of the alloy due to the strong gettering ability of titanium. Quantification of the soft x-ray photoelectron spectra highlights the formation of three tungsten oxidation environments, attributed to WO

Journal article

Hartley P, Egdell RG, Zhang KHL, Hohmann M, Piper LFJ, Morgan DJ, Scanlon DO, Williamson BAD, Regoutz Aet al., 2021, Experimental and Theoretical Study of the Electronic Structures of Lanthanide Indium Perovskites LnInO(3), JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 125, Pages: 6387-6400, ISSN: 1932-7447

Journal article

Swallow JEN, Palgrave RG, Murgatroyd PAE, Regoutz A, Lorenz M, Hassa A, Grundmann M, von Wenckstern H, Varley JB, Veal TDet al., 2021, Indium Gallium Oxide Alloys: Electronic Structure, Optical Gap, Surface Space Charge, and Chemical Trends within Common-Cation Semiconductors, ACS APPLIED MATERIALS & INTERFACES, Vol: 13, Pages: 2807-2819, ISSN: 1944-8244

Journal article

Regoutz A, Wolinska MS, Fernando NK, Ratcliff LEet al., 2021, A combined density functional theory and x-ray photoelectron spectroscopy study of the aromatic amino acids, Electronic Structure, Vol: 2, Pages: 1-11, ISSN: 2516-1075

Amino acids are essential to all life. However, our understanding of some aspects of their intrinsic structure, molecular chemistry, and electronic structure is still limited. In particular the nature of amino acids in their crystalline form, often essential to biological and medical processes, faces a lack of knowledge both from experimental and theoretical approaches. An important experimental technique that has provided a multitude of crucial insights into the chemistry and electronic structure of materials is x-ray photoelectron spectroscopy. While the interpretation of spectra of simple bulk inorganic materials is often routine, interpreting core level spectra of complex molecular systems is complicated to impossible without the help of theory. We have previously demonstrated the ability of density functional theory to calculate binding energies of simple amino acids, using ΔSCF implemented in a systematic basis set for both gas phase (multiwavelets) and solid state (plane waves) calculations. In this study, we use the same approach to successfully predict and rationalise the experimental core level spectra of phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), and histidine (His) and gain an in-depth understanding of their chemistry and electronic structure within the broader context of more than 20 related molecular systems. The insights gained from this study provide significant information on the nature of the aromatic amino acids and their conjugated side chains.

Journal article

Swallow JEN, Vorwerk C, Mazzolini P, Vogt P, Bierwagen O, Karg A, Eickhoff M, Schoermann J, Wagner MR, Roberts JW, Chalker PR, Smiles MJ, Murgatroyd P, Razek SA, Lebens-Higgins ZW, Piper LFJ, Jones LAH, Thakur PK, Lee T-L, Varley JB, Furthmueller J, Draxl C, Veal TD, Regoutz Aet al., 2020, Influence of Polymorphism on the Electronic Structure of Ga2O3, CHEMISTRY OF MATERIALS, Vol: 32, Pages: 8460-8470, ISSN: 0897-4756

Journal article

Minh HT, Malik AM, Duerrschnabel M, Regoutz A, Thakur P, Lee T-L, Perera D, Molina-Luna L, Albe K, Rohrer J, Birkel CSet al., 2020, Experimental and theoretical investigation of the chemical exfoliation of Cr-based MAX phase particles, DALTON TRANSACTIONS, Vol: 49, Pages: 12215-12221, ISSN: 1477-9226

Journal article

Mielewczyk-Gryn A, Wachowski S, Witkowska A, Dzierzgowski K, Skubida W, Swierczek K, Regoutz A, Payne DJ, Hull S, Zhang H, Abrahams I, Gazda Met al., 2020, Antimony substituted lanthanum orthoniobate proton conductor - Structure and electronic properties, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 103, Pages: 6575-6585, ISSN: 0002-7820

Journal article

Berens J, Bichelmaier S, Fernando NK, Thakur PK, Lee T-L, Mascheck M, Wiell T, Eriksson SK, Matthias Kahk J, Lischner J, Mistry M, Aichinger T, Pobegen G, Regoutz Aet al., 2020, Effects of nitridation on SiC/SiO(2)structures studied by hard X-ray photoelectron spectroscopy, JOURNAL OF PHYSICS-ENERGY, Vol: 2, ISSN: 2515-7655

Journal article

Leung AHM, García-Trenco A, Phanopoulos A, Regoutz A, Schuster ME, Pike SD, Shaffer MSP, Williams CKet al., 2020, Cu/M:ZnO (M = Mg, Al, Cu) colloidal nanocatalysts for the solution hydrogenation of carbon dioxide to methanol, Journal of Materials Chemistry A, Vol: 8, Pages: 11282-11291, ISSN: 2050-7488

Doped-ZnO nanoparticles, capped with dioctylphosphinate ligands, are synthesised by the controlled hydrolysis of a mixture of organometallic precursors. Substitutional doping of the wurtzite ZnO nanoparticles with 5 mol% Mg(II), Al(III) and Cu(I) is achieved by the addition of sub-stoichiometric amounts of the appropriate dopant [(n-butyl)(sec-butyl)magnesium, triethylaluminium or mesitylcopper] to diethylzinc in the precursor mixture. After hydrolysis, the resulting colloidal nanoparticles (sizes of 2–3 nm) are characterised by powder X-ray crystallography, transmission electron microscopy, inductively-coupled plasma optical emission spectrometry and X-ray photoelectron spectroscopy. A solution of the doped-ZnO nanoparticles and colloidal Cu(0) nanoparticles [M:ZnO : Cu = 1 : 1] are applied as catalysts for the hydrogenation of CO2 to methanol in a liquid-phase continuous flow stirred tank reactor [210 °C, 50 bar, CO2 : H2 = 1 : 3, 150 mL min−1, mesitylene, 20 h]. All the catalyst systems display higher rates of methanol production and better stability than a benchmark heterogeneous catalyst, Cu–ZnO–Al2O3 [480 μmol mmolmetal−1 h−1], with approximately twice the activity for the Al(III)-doped nanocatalyst. Despite outperforming the benchmark catalyst, Mg(II) doping is detrimental towards methanol production in comparison to undoped ZnO. X-Ray photoelectron spectroscopy and transmission electron microscopy analysis of the most active post-catalysis samples implicate the migration of Al(III) to the catalyst surface, and this surface enrichment is proposed to facilitate stabilisation of the catalytic ZnO/Cu interfaces.

Journal article

Williamson BAD, Featherstone TJ, Sathasivam SS, Swallow JEN, Shiel H, Jones LAH, Smiles MJ, Regoutz A, Lee T-L, Xia X, Blackman C, Thakur PK, Carmalt CJ, Parkin IP, Veal TD, Scanlon DOet al., 2020, Resonant Ta Doping for Enhanced Mobility in Transparent Conducting SnO2, CHEMISTRY OF MATERIALS, Vol: 32, Pages: 1964-1973, ISSN: 0897-4756

Journal article

Pi JM, Stella M, Fernando NK, Lam AY, Regoutz A, Ratcliff LEet al., 2020, Predicting core level photoelectron spectra of amino acids using density functional theory., Journal of Physical Chemistry Letters, Vol: 11, Pages: 2256-2262, ISSN: 1948-7185

Core level photoelectron spectroscopy is a widely used technique to study amino acids. Interpretation of the individual contributions from functional groups and their local chemical environments to overall spectra requires both high-resolution reference spectra and theoretical insights, for example, from density functional theory calculations. This is a particular challenge for crystalline amino acids due to the lack of experimental data and the limitation of previous calculations to gas phase molecules. Here, a state of the art multiresolution approach is used for high-precision gas phase calculations and to validate core hole pseudopotentials for plane-wave calculations. This powerful combination of complementary numerical techniques provides a framework for accurate ΔSCF calculations for molecules and solids in systematic basis sets. It is used to successfully predict C and O 1s core level spectra of glycine, alanine, and serine and identify chemical state contributions to experimental spectra of crystalline amino acids.

Journal article

Swallow JEN, Williamson BAD, Sathasivam S, Birkett M, Featherstone TJ, Murgatroyd PAE, Edwards HJ, Lebens-Higgins ZW, Duncan DA, Farnworth M, Warren P, Peng N, Lee T-L, Piper LFJ, Regoutz A, Carmalt CJ, Parkin IP, Dhanak VR, Scanlon DO, Veal TDet al., 2020, Resonant doping for high mobility transparent conductors: the case of Mo-doped In2O3, MATERIALS HORIZONS, Vol: 7, Pages: 236-243, ISSN: 2051-6347

Journal article

Hankin A, Bedoya-Lora FE, Alexander JC, Regoutz A, Kelsall GHet al., 2019, Flat band potential determination: avoiding the pitfalls, Journal of Materials Chemistry A, Vol: 7, Pages: 26162-26176, ISSN: 2050-7488

The flat band potential is one of the key characteristics of photoelectrode performance. However, its determination on nanostructured materials is associated with considerable uncertainty. The complexity, applicability and pitfalls associated with the four most common experimental techniques used for evaluating flat band potentials, are illustrated using nanostructured synthetic hematite (α-Fe2O3) in strongly alkaline solutions as a case study. The motivation for this study was the large variance in flat band potential values reported for synthetic hematite electrodes that could not be justified by differences in experimental conditions, or by differences in their charge carrier densities. We demonstrate through theory and experiments that different flat band potential determination methods can yield widely different results, so could mislead the analysis of the photoelectrode performance. We have examined: (a) application of the Mott–Schottky (MS) equation to the interfacial capacitance, determined by electrochemical impedance spectroscopy as a function of electrode potential and potential perturbation frequency; (b) Gärtner–Butler (GB) analysis of the square of the photocurrent as a function of electrode potential; (c) determination of the potential of transition between cathodic and anodic photocurrents during slow potentiodynamic scans under chopped illumination (CI); (d) open circuit electrode potential (OCP) under high irradiance. Methods GB, CI and OCP were explored in absence and presence of H2O2 as hole scavenger. The CI method was found to give reproducible and the most accurate results on hematite but our overall conclusion and recommendation is that multiple methods should be employed for verifying a reported flat band potential.

Journal article

Shankar R, Sachs M, Francas L, Lubert-Perquel D, Kerherve G, Regoutz A, Petit Cet al., 2019, Porous boron nitride for combined CO2 capture and photoreduction, Journal of Materials Chemistry A, Vol: 7, Pages: 23931-23940, ISSN: 2050-7488

Porous and amorphous materials are typically not employed for photocatalytic purposes, like CO2 photoreduction, as their high number of defects can lead to low charge mobility and favour bulk electron–hole recombination. Yet, with a disordered nature can come porosity, which in turn promotes catalyst/reactant interactions and fast charge transfer to reactants. Here, we demonstrate that moving from h-BN, a well-known crystalline insulator, to amorphous BN, we create a semiconductor, which is able to photoreduce CO2 in the gas/solid phase, under both UV-vis and pure visible light and ambient conditions, without the need for cocatalysts. The material selectively produces CO and maintains its photocatalytic stability over several catalytic cycles. The performance of this un-optimized material is on par with that of TiO2, the benchmark in the field. For the first time, we map out experimentally the band edges of porous BN on the absolute energy scale vs. vacuum to provide fundamental insight into the reaction mechanism. Owing to the chemical and structural tunability of porous BN, these findings highlight the potential of porous BN-based structures for photocatalysis particularly solar fuel production.

Journal article

Mielewczyk-Gryn A, Wachowski S, Przesniak-Welenc M, Dzierzgowski K, Regoutz A, Payne DJ, Gazda Met al., 2019, Water uptake analysis of acceptor-doped lanthanum orthoniobates, Journal of Thermal Analysis and Calorimetry: an international forum for thermal studies, Vol: 138, Pages: 225-232, ISSN: 1588-2926

In this work, lanthanum orthoniobates doped with either antimony, calcium, or both have been synthesized and studied. The water uptake of the investigated materials has been analyzed by means of thermogravimetric studies. The results show the difference between the thermodynamics of hydration between the lanthanum orthoniobate system and other proton conducting ceramics. The relation between the water uptake and effective acceptor doping for the investigated system has been found, and the energetics of the water uptake relation are discussed.

Journal article

Mezzavilla S, Katayama Y, Rao R, Hwang J, Regoutz A, Shao-Horn Y, Chorkendorff I, Stephens IELet al., 2019, Activity-or Lack Thereof-of RuO2-Based Electrodes in the Electrocatalytic Reduction of CO2, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 17765-17773, ISSN: 1932-7447

Journal article

Twyman N, Tetzner K, Anthopoulos T, Payne D, Regoutz Aet al., 2019, Rapid photonic curing of solution-processed In2O3 layers on flexible substrates, Applied Surface Science, Vol: 479, Pages: 974-979, ISSN: 0169-4332

In2O3 is one of the most important semiconducting metal oxides primarily because of its wide band gap, high electron mobility and processing versatility. To this end, high-quality thin films of In2O3 can be prepared using scalable and inexpensive solution-based deposition methods, hence making it attractive for application in a number of emerging electronic applications. However, traditional solution processing often requires high temperature and lengthy annealing steps, making it impossible to use in combination with temperature-sensitive plastic substrates, which would be desired for numerous emerging flexible device applications. Here, rapid photonic curing of In2O3 layers is explored as an alternative to thermal annealing. Oxide thin films are successfully prepared on a range of substrates, including glass, polyimide, and polyethylene naphthalate. The effect of substrate and post-processing treatment on the morphology, surface chemistry, and electronic properties is investigated by atomic force microscopy and X-ray photoelectron spectroscopy. Systematic trends are identified, particularly in the degree of conversion of the precursor and its influence on the electronic structure.

Journal article

Robinson MDM, Oropeza FE, Cui M, Zhang KHL, Hohmann MV, Payne DJ, Egdell RG, Regoutz Aet al., 2019, Electronic structure of lanthanide-doped bismuth vanadates: A systematic study by x-ray photoelectron and optical spectroscopies, Journal of Physical Chemistry C, Vol: 123, Pages: 8484-8499, ISSN: 1932-7447

Monoclinic BiVO 4 has emerged in recent years as one of the most promising materials for photocatalytic evolution of oxygen under solar irradiation. However, it is in itself unable to phototcatalyze reduction of water to hydrogen due to the placement of the conduction band edge below the potential required for H 2 O/H 2 reduction. As a consequence, BiVO 4 only finds application in a hybrid system. Very recently, tetragonal lanthanide-doped BiVO 4 powders have been shown to be able to both reduce and to oxidize water under solar irradiation, but to date there has been no comprehensive study of the electronic properties of lanthanide-doped bismuth vanadates aimed at establishing the systematic trends in the electronic structure in traversing the lanthanide series. Here, the accessible family of lanthanide-doped BiVO 4 quaternary oxides of stoichiometry Bi 0.5 Ln 0.5 VO 4 (Ln = La to Lu, excluding Pm) has been studied by X-ray powder diffraction, X-ray photoemission spectroscopy, and diffuse reflectance optical spectroscopy. The compounds all adopt the tetragonal zircon structure, and lattice parameters decrease monotonically in traversing the lanthanide series. At the same time, there is an increased peak broadening in the diffraction patterns as the mismatch in ionic radius between Bi 3+ and the Ln 3+ ions increases across the series. Valence band X-ray photoemission spectra show that the final state 4f n-1 structure associated with ionization of lanthanide 4f n states is superimposed on the valence band structure of BiVO 4 in the quaternary materials: in the case of the Ce-, Pr- and Tb-doped BiVO 4 , 4f-related states appear above the top of the main valence band of BiVO 4 and account for the small bandgap in the Ce compound. In all cases, the 4f structure is characteristic of the lanthanide element in the Ln(III) oxidation state. Vanadium 2p and lanthanide 3d or 4d core level photoelectron spectra of those compounds where the lanthanide may in principle adopt a hig

Journal article

Gusken NA, Lauri A, Li Y, Matsui T, Doiron B, Bower R, Regoutz A, Mihai A, Petrov PK, Oulton RF, Cohen LF, Maier SAet al., 2019, TiO2-x-enhanced IR hot carrier based photodetection in metal thin film-si junctions, ACS Photonics, Vol: 6, Pages: 953-960, ISSN: 2330-4022

We investigate titanium nitride (TiN) thin film coatings on silicon for CMOS-compatible sub-bandgap charge separation upon incident illumination, which is a key feature in the vast field of on-chip photodetection and related integrated photonic devices. Titanium nitride of tunable oxidation distributions serves as an adjustable broadband light absorber with high mechanical robustness and strong chemical resistivity. Backside-illuminated TiN on p-type Si (pSi) constitutes a self-powered and refractory alternative for photodetection, providing a photoresponsivity of about ∼1 mA/W at 1250 nm and zero bias while outperforming conventional metal coatings such as gold (Au). Our study discloses that the enhanced photoresponse of TiN/pSi in the near-infrared spectral range is directly linked to trap states in an ultrathin TiO2–x interfacial interlayer that forms between TiN and Si. We show that a pSi substrate in conjunction with a few nanometer thick amorphous TiO2–x film can serve as a platform for photocurrent enhancement of various other metals such as Au and Ti. Moreover, the photoresponse of Au on a TiO2–x/pSi platform can be increased to about 4 mA/W under 0.45 V reverse bias at 1250 nm, allowing for controlled photoswitching. A clear deviation from the typically assumed Fowler-like response is observed, and an alternative mechanism is proposed to account for the metal/semiconductor TiO2–x interlayer, capable of facilitating hole transport.

Journal article

Lee W-C, Wahila MJ, Mukherjee S, Singh CN, Eustance T, Regoutz A, Paik H, Boschker JE, Rodolakis F, Lee T-L, Schlom DG, Piper LFJet al., 2019, Cooperative effects of strain and electron correlation in epitaxial VO2 and NbO2, Publisher: AMER INST PHYSICS

Working paper

Regoutz A, Ganose AM, Blumenthal L, Schlueter C, Lee T-L, Kieslich G, Cheetham AK, Kerherve G, Huang Y-S, Chen R-S, Vinai G, Pincelli T, Panaccione G, Zhang KHL, Egdell RG, Lischner J, Scanlon DO, Payne DJet al., 2019, Insights into the electronic structure of OsO2 using soft and hard x-ray photoelectron spectroscopy in combination with density functional theory, Physical Review Materials, Vol: 3, ISSN: 2475-9953

Theory and experiment are combined to gain an understanding of the electronic properties of OsO2, a poorly studied metallic oxide that crystallizes in the rutile structure. Hard and soft valence-band x-ray photoemission spectra of OsO2 single crystals are in broad agreement with the results of density-functional-theory calculations, aside from a feature shifted to high binding energy of the conduction band. The energy shift corresponds to the conduction electron plasmon energy measured by reflection electron energy loss spectroscopy. The plasmon satellite is reproduced by many-body perturbation theory.

Journal article

Davies DW, Walsh A, Mudd JJ, McConville CF, Regoutz A, Kahk JM, Payne DJ, Dhanak VR, Hesp D, Pussi K, Lee T-L, Egdell RG, Zhang KHLet al., 2019, Identification of lone-pair surface states on indium oxide, Journal of Physical Chemistry C, Vol: 123, Pages: 1700-1709, ISSN: 1932-7447

Indium oxide is widely used as a transparent electrode in optoelectronic devices and as a photocatalyst with activity for reduction of CO2. However, very little is known about the structural and electronic properties of its surfaces, particularly those prepared under reducing conditions. In this report, directional “lone-pair” surface states associated with filled 5s2 orbitals have been identified on vacuum-annealed In2O3(111) through a combination of hard and soft X-ray photoemission spectroscopy and density functional theory calculations. The lone pairs reside on indium ad-atoms in a formal +1 oxidation state, each of which traps two electrons into a localized hybrid orbital protruding away from the surface and lying just above the valence band maximum in photoemission spectra. The third electron associated with the ad-atoms is delocalized into the conduction band, thus producing the surface electron accumulation layer identified previously on vacuum-annealed In2O3(111) (1 × 1) surfaces. The surface structure is further supported by low-energy electron diffraction, but there is no chemical shift in indium core level X-ray photoelectron spectra between surface In(I) ad-atoms and bulk In(III). The 5s2 lone pairs confer Lewis basicity on the surface In sites and may have a pronounced impact on the catalytic or photocatalytic activity of reduced In2O3.

Journal article

Jolly P, Rainbow J, Regoutz A, Estrela P, Moschou Det al., 2019, A PNA-based Lab-on-PCB diagnostic platform for rapid and high sensitivity DNA quantification., Biosensors and Bioelectronics, Vol: 123, Pages: 244-250, ISSN: 0956-5663

We report the development of a Lab-on-PCB DNA diagnostic platform, exploiting peptide nucleic acid (PNA) sequences as probes. The study demonstrates the optimization and characterization of two commercial PCB manufacturing gold electroplating processes for biosensing applications. Using an optimized ratio of PNA with a spacer molecule (MCH), the lowest limit of detection (LoD) to date for PCB-based DNA biosensors of 57 fM is reported. The study also showcases a fully integrated Lab-on-PCB microsystem designed for rapid detection, which employs PCB-integrated sample delivery, achieving DNA quantification in the 0.1-100 pM range for 5 μL samples analyzed within 5 min under continuous flow. The demonstrated biosensor proves the capability of PCB-based DNA biosensors for high sensitivity and paves the way for their integration in Lab-on-PCB DNA diagnostic microsystems.

Journal article

Ghiasi M, Hariki A, Winder M, Kuneš J, Regoutz A, Lee T-L, Hu Y, Rueff J-P, Groot FMFDet al., 2018, Hard x-ray 1$s$ and 2$p$ photoemission spectra: LDA+DMFT and cluster-model analysis

We study $1s$ and $2p$ hard x-ray photoemission spectra (XPS) in a series oflate transition metal oxides: Fe$_2$O$_3$ (3$d^{5}$), FeTiO$_3$ (3$d^{6}$), CoO(3$d^{7}$) and NiO (3$d^{8}$). The experimental spectra are analyzed with twotheoretical approaches: the MO$_6$ cluster model and the local densityapproximation (LDA) + dynamical mean-field theory (DMFT). Owing to the absenceof the core-valence multiplets and spin-orbit coupling, 1$s$ XPS is found to bea sensitive probe of chemical bonding and nonlocal charge-transfer screening,providing complementary information to 2$p$ XPS. The 1$s$ XPS spectra are usedto assess the accuracy of the $ab$-initio LDA+DMFT approach, developed recentlyto study the material-specific charge-transfer effects in core-level XPS.

Working paper

Regoutz A, Pobegen G, Aichinger T, 2018, Interface chemistry and electrical characteristics of 4H-SiC/SiO2 after nitridation in varying atmospheres, Journal of Materials Chemistry C, Vol: 6, Pages: 12079-12085, ISSN: 2050-7526

SiC has immense potential as the semiconductor for future metal–oxide–semiconductor (MOS) devices. One of the greatest advantages and disadvantages of SiC is its native oxide, SiO2. The ability to use established SiO2 processes to create a reliable dielectric directly on the SiC semiconductor is very desirable. However, the SiC/SiO2 interface exhibits high defect densities leading to detrimental effects on device performance. A variety of treatment processes, often in N-containing atmospheres, has been shown to compensate defects and increase device performance. However, information on the local chemistry at the interface after such processes is scarce, which limits the understanding of the interface and consequently the targeted improvement of device characteristics. The present work uses X-ray photoelectron spectroscopy (XPS) to systematically study the elemental distributions and chemical environments across the 4H-SiC/SiO2 interface after high temperature nitridation treatments in a variety of atmospheres. In particular the use of a NO/NH3 combinatorial process is of great interest as it influences the defect chemistry on both the oxide and carbide side of the interface. We are able to identify N–C–Si environments as the dominant defect states at the interface. The XPS results are correlated with electrical and reflective index measurements, providing new, detailed insights into the relationship between interface chemistry and device behaviour.

Journal article

Regoutz A, Kerherve G, Villar-Garcia I, Williams CK, Payne DJet al., 2018, The influence of oxygen on the surface interaction between CO2 and copper studied by ambient pressure X-ray photoelectron spectroscopy, SURFACE SCIENCE, Vol: 677, Pages: 121-127, ISSN: 0039-6028

Journal article

Lu H, Andrei V, Jenkinson KJ, Regoutz A, Li N, Creissen CE, Wheatley AEH, Hao H, Reisner E, Wright DS, Pike SDet al., 2018, Single-source bismuth (transition metal) polyoxovanadate precursors for the scalable synthesis of doped BiVO4 photoanodes, Advanced Materials, Vol: 30, ISSN: 0935-9648

Single-source precursors are used to produce nanostructured BiVO4 photoanodes for water oxidation in a straightforward and scalable drop-casting synthetic process. Polyoxometallate precursors, which contain both Bi and V, are produced in a one-step reaction from commercially available starting materials. Simple annealing of the molecular precursor produces nanocrystalline BiVO4 films. The precursor can be designed to incorporate a third metal (Co, Ni, Cu, or Zn), enabling the direct formation of doped BiVO4 films. In particular, the Co- and Zn-doped photoanodes show promise for photoelectrochemical water oxidation, with photocurrent densities >1 mA cm-2 at 1.23 V vs reversible hydrogen electrode (RHE). Using this simple synthetic process, a 300 cm2 Co-BiVO4 photoanode is produced, which generates a photocurrent of up to 67 mA at 1.23 V vs RHE and demonstrates the scalability of this approach.

Journal article

Regoutz A, Mascheck M, Wiell T, Eriksson S, Liljenberg C, Tetzner K, Williamson B, Scanlon D, Palmgren Pet al., 2018, A novel laboratory-based hard x-ray photoelectron spectroscopy system, Review of Scientific Instruments, Vol: 89, ISSN: 0034-6748

Hard X-ray photoelectron spectroscopy (HAXPES) has seen continuous development since the first experiments in the 1970s. HAXPES systems are predominantly located at synchrotron sources due to low photoionization cross sections necessitating high X-ray intensities, which limits the technique’s availability to a wide range of users and potential applications. Here, a new laboratory-based instrument capable of delivering monochromated X-rays with an energy of 9.25 keV and a microfocused 30 × 45 μm2 X-ray spot is introduced. The system gives an excellent energy resolution of below 500 meV coupled with good X-ray intensity. It allows stable measurements under grazing incidence conditions to maximise signal intensities. This article outlines the instrument behavior, showcases applications including bulk and multilayer measurements, and describes the overall performance of the spectrometer. This system presents an alternative to synchrotron-based experimental end stations and will help expand the number and range of HAXPES experiments performed in the future.

Journal article

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